Many untreated or uncoated polymeric films, such as films made from isotactic polypropylene, may not provide for acceptable adherence of inks or adhesives without special treating or coating. Coating and treating polymer films greatly improves their usefulness and functionality. However, when both sides of a film are treated and/or coated to increase surface energy, severe interfacial blocking problems can arise when the film is rolled or stacked. To be useful, processable, and functional, a topside surface of a polymer film should not block to a back-side surface.
In polymer films useful for labeling applications, it is desirable that a film is suitably printable on one surface of the film, while the other surface of the film suitably bonds with an adhesive that is useful for attaching the film or label to a container. Solutions to the blocking problem commonly provide for printing and applying an adhesive to the same surface. Thereby, only one surface of a film need possess an increased surface energy, thus controlling or avoiding blocking problems. To avoid blocking problems, films prepared for use as label facestock, particularly pressure sensitive facestock, may be coated on one surface with a coating that enhances printability, adhesion, mar resistance, and/or pasteurization resistance. The opposite side of such facestock film may be untreated.
Alternatively, some label facestock has a treated or coated topside surface for receiving printing inks but do not include a treatment or coating on the adhesive-receiving surface (for example, Clear PSA4 manufactured by ExxonMobil Oil Corporation). A printer or converter may later corona-treat the adhesive-receiving surface immediately before applying an adhesive and a release liner to the facestock.
Label facestocks that provide a limited but acceptable degree of blocking possess a print-side/top-side coating and a treated but uncoated adhesive-receiving/back-side surface. Treatment of the adhesive-receiving surface by flame or corona discharge may be used on the adhesive-receiving side to render the uncoated plastic surface receptive to adhesives. For example, U.S. Pat. Nos. 5,380,587 and 5,382,473 to Musclow, et al. disclose a multilayer packaging or label stock films having excellent printability and non-blocking characteristics to a treated, but uncoated, polyolefin surface. Such films may be challenging and rigorous to produce. Treatment has to be carefully controlled in order to prevent blocking or fitness for use problems. Too much treatment can generate blocking problems. Too little treatment would make the film not fit for use and require converter re-treatment. Film flatness must be well controlled as well as some variability can generate high pressure areas prone to create blocking.
US 20070244880 discloses coated polymer films comprising a polymeric substrate including a first side and a second side; a back-side coating on the second side of the substrate, the back-side coating comprising an ionomer; particles of a colloidal mineral, a majority by weight of the colloidal mineral particles having an overall mean diameter of no greater than about 0.1 micron; and a front-side coating on the first side of the substrate, wherein the front-side coating is printable.
Nevertheless, the polymeric labeling industry still needs an opaque film with robust adhesive anchorage and that has acceptable resistance to blocking to a printable topside coating, particularly over a wider range of exposure times to high temperature and high humidity conditions. Moreover, there is a need to provide such a film having a low carbon footprint and a method of making such a film, the method also having a low carbon footprint.